Effects and Types of Anesthetics

Effects and Types of Anesthetics
Anesthetics are depressant drugs that cause a total or
partial loss of the sense of pain. The effect an anesthetic has
on the body depends on several factors. What type of anesthetic
is used determines the effect along with the dosage and a person
(or animal?s) body weight.
The word anesthesia was first introduced by Oliver Wendell
Holmes in 1846 about four weeks after the first demonstration of
ether anesthesia at the Massachusetts General Hospital. Ether
was the first type of anesthesia used and was demonstrated as a
means of allowing a patient to be unconscious and free from
surgical pain.
Stage one is known as analgesia and results from an increase
in circulating endorphins. There is a mild depression of
cortical centers and this type of anesthesia is also known as
twilight sleep.
Stage two is characterized by a loss of consciousness. It
is a critical period because delirium and increased involuntary
activity, as well as hypersecretion, can occur. It is best to
get through stage one and stage two as quickly as possible and
this stage, along with stage one, are known as induction.
Stage three is the stage of anesthesia known as surgical
anesthesia, and most surgical procedures are performed in this
stage. There is usually a loss of spinal reflexes and muscle
tone.
Stage four is an undesirable stage and is characterized by
respiratory depression and other manifestations of overdose.
Most general anesthetics are non-specific agents, meaning
that their activity depends on their lipid solubility rather that
their structure. Inhaled and exhaled gas containing the agents
equilibrates with the lung tissue, and then with the blood. In
the brain, the agent equilibrates between the blood and neural
tissue, depressing neurons and causing the pharmacological
effect.

Types of Anesthesia

Though ether was the first type of anesthesia, there are now
many different types. Ether, along with chloroform, are known as
the anesthetics from hell because they have all of the negative
traits of this class of drugs. Ethyl ether is potent and fairly
safe, but it is also flammable and explosive. It forms peroxides
and it produces a very unpleasant induction phase. Also, it is
irritating and causes nausea and vomiting during recovery.
Chloroform is just as potent and relaxes the skeletal muscle
fairly effectively, but has a narrow margin of safety, produces
liver and kidney toxicity, and has been known to fairly
frequently cause cardiac arrest. In addition, it can also cause
severe hypertension.
Another type of general anesthetic agent is non halogenated
hydrocarbons. All of these work well and the longer the chain,
the higher the potency. However, these have a tendency to
produce cardiovascular toxicity. Cyclopropane is the only one
still in use and is explosive.
Ethyl ether was the first anesthetic, but is not used
anymore because of its negative effects, but other ethers came
along throughout the past century and a half as well. Like
hydrocarbons, the longer the chain, the more potent the
anesthetic. However, the longer the chain, the higher the
toxicity. Also having a longer chain reduces induction time.
Ethyl ether is very rarely used and divinyl ether is explosive
and produces deep anesthesia too quickly.
Another type of general anesthetic is halogenated
hydrocarbons. When a halogen is added to an anesthesia,
flammability is greatly reduced, and in some cases, eliminated.
In addition, the halogen can also add potency. Depending on the
halogen, some of these compounds can cause arrhythmia and/or
renal or hepatic toxicity. Compounds containing only bromine are
usually not useful and compounds containing only chlorine are
limited in use, are toxic, and can cause arrhythmia. The best of
the chlorinated agents are ethyl chloride and trichloroethylene.
Fluorinated hydrocarbons are the most useful general
anesthetics, and were first discovered as offshoots of the
nuclear weapons program. Adding a fluorine to an anesthetic
decreases flammability and boiling point. It also decreases the
rate of catechol- induced arrhythmia (these increase as the size
of the halogen increases). Listed below are a few different
types of fluorinate hydrocarbons:
Halothane (Fluothane) was the first fluorinated hydrocarbon
to be used. It is a poor muscle relaxant, and has some toxicity
and has been shown to cause catechol- induced arrhythmia.
Methoxyflurane (Penthrane) is somewhat better than the
above, but still causes some arrhythmia and toxicity. It also
causes a slow induction period.
Enflurane (Enthrane) is a pretty good anesthetic in stage
one (see topic below).
Isoflurane (Forane) is the best general anesthetic found so
far and has no common ill effects.

Another type of general anesthetics is nitrous oxide. This
is the least toxic anesthetic, but is also the least potent. It
causes good analgesia. but is a poor muscle relaxant.
Ketamine hydrochloride is also an anesthetic agent and is
derived from phencyclidine. It acts like a volatile anesthetic
agent and is potent, quickly acting, and has a short duration.
It is usually only used for children under 16 because about 27%
of those over 16 have wild dreams and hallucinations during
emergence that can be rather dangerous and unpleasant.

Conclusion

Throughout the past century and a half, there have been many
advances in all fields of medicine. Anesthetics have, too,
changed tremendously. Although whenever an anesthetic is used, a
risk is involved, anesthetics have come a long way since 1846 and
are fairly safe now. They are used in most surgical procedures
and have allowed may new types of surgical procedures to take
place. They have contributed greatly to our wonderful world of
medicine.

Effects and Types of Anesthetics 9 of 10 on the basis of 894 Review.